Hello Mari and welcome to justanswer.com
I can help you but first I need you to answer a couple of questions. If you set the climate control to Lo then bring it to high do you feel a difference in the outlet air temp? Do you have the touch screen or standard controls? Also turn off the climate control and turn off the engine. Then start your engine and turn on the a/c. You should hear an audiable click from the driver side of the engine compartment. That is the a/c compressor. Let me know if you can hear it engage?
If you feel a difference in temp then it sounds like the heater control valve is not sticking and the evap and other temps sensors are working. You may just have a low refrigerant charge. If the charge is too low the compressor will not turn on cause of low pressure.
The it is possible that the heater valve is sticking slightly open or that the climate control module is not closing the valve. This is going to be difficult to diagnose your self but we can try. What I would do is first pinch off the heater hoses going to the core. If the air gets colder then it's a heater valve or valve circuit causing the problem.
Thanks for the accept and for using justanswer.com.